1. Field of the Invention
The present invention relates to fluid pumping arrangements for wells, intended to give an increased rate of recovery and/or better efficiency in pumping. The invention is particularly valuable for oil wells, but may be used for other liquids such as water.
2. Prior Art
Presently, most oil is pumped from oil wells using down-hole reciprocating pumps. Such a pump has a well head pumping mechanism causing reciprocating movement of a sucker rod which operates the down hole pump. The latter pump has a piston rod operating a piston slidable within a barrel, and has valve means in the piston and barrel which cause the oil to be lifted on each upstroke of the sucker rod. With a single-acting pump of this kind the rod operates almost entirely in tension. Such single acting pumps cannot maintain a steady flow of oil, and the need to accelerate a long column of oil in the well with each stroke is a major factor in the energy required for pumping oil or other liquids.
Another source of losses in conventional reciprocating pumps is the frictional resistance between the sucker rods and the column of liquid in which they move, which may be substantial given that the column of liquid may be hundreds of feet long.
Proposals have been made for double acting pumps which could give a more even delivery of oil by producing an output both on the upstroke and the downstroke; such proposals are shown for example in the following U.S. patents:
U.S. Pat. No. 6,585,049, issued Jul. 1, 2003 to Lenick, Sr., and
U.S. Pat. No. 5,873,411, issued Feb. 23, 1999 to Prentiss.
Proposals such as these, for double acting pumps, are either complicated, as in the Prentiss patent, or, as with the Lenick, Sr. patent, they require the sucker rods or their equivalent to apply downwards forces, which means these rods either have to be rigid, or have to be heavily weighted at the bottom so that they are not subjected to significant compressive forces. Compressive forces are normally avoided or minimized since these rods may be very long.
Another form of downhole pump is a rotary auger-type pump, sometimes termed a “progressive cavity pump”, as manufactured by Moyno Oilfields Products of Tulsa, Okla., which can give a substantially constant output. However, such pumps are less efficient than is desirable.